Cylindrical seals are widely used to prevent loss of working fluid pressure and to improve working performance, such as in pistons used in pneumatic and hydraulic systems of gas turbine engines or in other applications such as engine cylinders of internal combustion engines. Conventional cylindrical seals such as piston ring seal designs typically include the use of a piston ring as a seal in reciprocating, rotating and static conditions. The simplest form of a conventional piston ring has a rectangular cross-section with a primary sealing contact between an outer-diameter surface of the ring and an inner surface of a cylinder, and a secondary sealing contact between a side of the ring and a lower pressure side of a groove in which the ring is supported. The primary sealing contact between the outer-diameter surface and the inner surface of the cylinder is established when the ring is installed and is maintained by a pre-tension of the piston seal ring. The secondary sealing contact, however, cannot be achieved until a working fluid pressure is built up in the cylinder causing leakage around the sides and the inner-diameter surface of the ring. The flow of working fluid through the small clearances around the ring causes a pressure drop across the ring. The unbalanced force seats the ring against the lower pressure side of the groove and therefore establishes the secondary sealing contact. However, the secondary sealing method can lead to sealing variability and undesirable, inconsistent system response. Furthermore, conventional piston seal rings have a split end geometry that allows a leakage path in the radial direction. The leakage is usually minimized by a second piston seal ring positioned against the inner-diameter surface of the first piston seal ring such that the second piston seal ring blocks the end gap opening of the first piston seal ring. Care is required during installation to ensure the end gaps of the two piston seal rings are about 180 degrees apart.
Accordingly, improved cylindrical sealing is needed.